1. Field of the Invention
The present invention relates generally to broadcast data encryption that uses encryption keys, and more particularly to identifying keys that might have been discovered by hardware and/or software “clones” and that consequently have been compromised.
2. Description of the Related Art
The above-referenced applications disclose content guard systems for encrypting publicly sold music, videos, and other content. As set forth in the above-referenced applications, only authorized player-recorders can play and/or copy the content and only in accordance with rules established by the vendor of the content this way, pirated copies of content, which currently cost content providers billions of dollars each year, can be prevented.
In the content guard encryption method disclosed in the above-referenced applications, authorized player-recorders are issued software-implemented device keys from a matrix of device keys. Specifically, the matrix of device keys includes plural rows and columns, and each authorized player-recorder is issued a single key from each column. The keys can be issued simultaneously with each other or over time, but in any event, no player-recorder is supposed to have more than one device key per column of the matrix. Using its device keys, an authorized player-recorder can decrypt content that is contained on, e.g., media such as DVD disks, CDs, hard disk drives, flash memory, and so on that has been encrypted using the device keys. Because the player-recorder is an authorized device that is programmed to follow content guard rules, it then plays/copies the content in accordance with predefined rules that protect copyright owners' rights in digitized, publicly sold content.
Although providing a secure, reliable means to protect copyright in digitized content, the above-referenced applications also anticipate that clone devices might be constructed by pirates. Specifically, a clone device, which would not be programmed with the “rules” that legitimate player-recorders must follow, could use compromised device keys to decrypt content and then copy the content as many times as desired, selling the unauthorized copies or even providing them for free. In either case, the copyright owner loses. Accordingly, the above-referenced applications set forth various ways to deal with clone devices, once the compromised device keys have been identified.
The problem addressed by the present invention is, once a clone has been identified, how to determine which device keys it has and, thus, which keys have been compromised and thus require revoking in accordance with the previous applications. The present invention understands that a “clone” might be a hardware clone or might simply be a computer program that can be made available by, e.g., posting the program on the Internet. In either case, the present invention recognizes that it is desirable to identify the compromised keys possessed by the clone in an efficient way.